Power tools such as table saws, miter saws, band saws, hand-held circular saws, jointers, shapers, routers, and up-cut saws are used to cut and shape material. In most power tools a user simply flips a switch to start the tool. The switch closes a circuit so that electric current flows through the switch to a motor, and the motor moves a blade or cutter.
Power tools with active injury mitigation technology are controlled differently. Active injury mitigation technology refers to technology that detects contact or proximity between a person and a spinning blade or cutter, and then performs some predetermined action to mitigate injury, such as stopping and/or retracting the blade or cutter. Exemplary implementations of active injury mitigation technology are described in International Patent Application Publication No. WO 01/26064 A2, which is incorporated herein by reference. In tools equipped with active injury mitigation technology, a user also flips a switch to start the tool, but electric current does not typically flow through the switch to a motor. Instead, the switch requests or signals a microprocessor to start the motor, and the microprocessor then does so, provided any other conditions monitored by the microprocessor are satisfied.
This specification describes improved systems to control the operation of a power tool. The improved systems are particularly, but not exclusively, applicable to power tools with active injury mitigation technology. The improved systems, for example, control the supply of power to a motor, enhance reliability, and avoid unintended activation of the power tool.